An optical semiconductor module (optical module) wherein an optical fiber and a photoelectric conversion element are directly optically coupled (butt joint) without an optical element such as a lens interposed therebetween is described in JP-A 2005-43622. Region (a) of FIG. 5 is a cross-sectional view showing a conventional optical module prior to assembling. The optical module has a device array 1 and an optical ferrule 3.
The device array 1 has a coupling surface 5, and a plurality of photoelectric conversion elements 9 are arranged in one row (in a direction perpendicular to the plane of the drawing) at the center section of the coupling surface 5. A plurality of bumps 11, arranged parallel to the row of photoelectric conversion elements 9, function as connecting terminals for the elements. The ferrule 3 has a coupling surface 7, and a plurality of optical fiber insertion holes 15 for holding an optical fiber 13 in position are arranged in an open state in one row on the coupling surface 7. A plurality of electrical circuits (not shown) connected to the bumps 11 are arranged on the coupling surface 7 in parallel to the row direction of the insertion holes 15, and are continuously formed up to an orthogonal surface adjacent to the coupling surface 7. The ferrule 3 is made of a material containing a polyester resin, a PPS resin, or an epoxy resin.
The device array 1 and the ferrule 3 are arranged so that the coupling surface 5 and the coupling surface 7 face each other. The insertion hole 15 and the photoelectric conversion element are positionally aligned, and the bump 11 is secured to the electrical wiring, whereby the ferrule 3 and the device array 1 are integrally coupled. An appropriate length of a protective coating 19 is removed at a distal end of the optical fiber 13 to expose a glass fiber 21, and the optical fiber 13 is inserted into the insertion hole 15, so that the optical fiber 13 is optically coupled with the photoelectric conversion element 9. The optical fiber 13 is positionally aligned with the optical fiber ferrule 3 by a position-restricting hole section 15a in the insertion hole 15, the diameter of the hole section 15a being smaller on the coupling surface 7 side. Specifically, the optical fiber 13 is positionally aligned by the glass fiber 21 without the coating 19 being interposed therebetween.
Region (b) of FIG. 5 is an enlarged cross-sectional view of a section at the periphery of the distal end of the glass fiber 21 of a conventional optical module under assembling. When the glass fiber 21 is inserted into the insertion hole 15, the distal end of the glass fiber 21 may scrape against a plastic material that is softer than the glass fiber 21 such as an inner peripheral surface of the position-restricting hole section 15a. Fine particulate matter can be produced when the inner peripheral surface is so abraded. This particulate may also be present within the insertion hole 15. In some instances, the particulate 25 adheres to a surface 21a on the distal end of the glass fiber 21, reducing the efficiency of optical coupling with the device array 1, and degrading the anti-noise property of the optical module.